From: Thomas Gleixner <tglx@linutronix.de>
To: Nitesh Lal <nilal@redhat.com>
Cc: Jesse Brandeburg <jesse.brandeburg@intel.com>,
Robin Murphy <robin.murphy@arm.com>,
Ingo Molnar <mingo@kernel.org>,
linux-kernel@vger.kernel.org, intel-wired-lan@lists.osuosl.org,
jbrandeb@kernel.org, "frederic\@kernel.org" <frederic@kernel.org>,
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Marc Zyngier <maz@kernel.org>,
Neil Horman <nhorman@tuxdriver.com>
Subject: Re: [PATCH tip:irq/core v1] genirq: remove auto-set of the mask when setting the hint
Date: Tue, 18 May 2021 02:03:57 +0200 [thread overview]
Message-ID: <87im3gewlu.ffs@nanos.tec.linutronix.de> (raw)
In-Reply-To: <CAFki+Lkjn2VCBcLSAfQZ2PEkx-TR0Ts_jPnK9b-5ne3PUX37TQ@mail.gmail.com>
On Mon, May 17 2021 at 18:44, Nitesh Lal wrote:
> On Mon, May 17, 2021 at 4:48 PM Thomas Gleixner <tglx@linutronix.de> wrote:
>> The hint was added so that userspace has a better understanding where it
>> should place the interrupt. So if irqbalanced ignores it anyway, then
>> what's the point of the hint? IOW, why is it still used drivers?
>>
> Took a quick look at the irqbalance repo and saw the following commit:
>
> dcc411e7bf remove affinity_hint infrastructure
>
> The commit message mentions that "PJ is redesiging how affinity hinting
> works in the kernel, the future model will just tell us to ignore an IRQ,
> and the kernel will handle placement for us. As such we can remove the
> affinity_hint recognition entirely".
No idea who PJ is. I really love useful commit messages. Maybe Neil can
shed some light on that.
> This does indicate that apparently, irqbalance moved away from the usage of
> affinity_hint. However, the next question is what was this future
> model?
I might have missed something in the last 5 years, but that's the first
time I hear about someone trying to cleanup that thing.
> I don't know but I can surely look into it if that helps or maybe someone
> here already knows about it?
I CC'ed Neil :)
>> Now there is another aspect to that. What happens if irqbalanced does
>> not run at all and a driver relies on the side effect of the hint
>> setting the initial affinity. Bah...
>>
>
> Right, but if they only rely on this API so that the IRQs are spread across
> all the CPUs then that issue is already resolved and these other drivers
> should not regress because of changing this behavior. Isn't it?
Is that true for all architectures?
>> While none of the drivers (except the perf muck) actually prevents
>> userspace from fiddling with the affinity (via IRQF_NOBALANCING) a
>> deeper inspection shows that they actually might rely on the current
>> behaviour if irqbalanced is disabled. Of course every driver has its own
>> convoluted way to do that and all of those functions are well
>> documented. What a mess.
>>
>> If the hint still serves a purpose then we can provide a variant which
>> solely applies the hint and does not fiddle with the actual affinity,
>> but if the hint is useless anyway then we have a way better option to
>> clean that up.
>>
>
> +1
= 1
Thanks,
tglx
next prev parent reply other threads:[~2021-05-18 0:04 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-01 2:18 [PATCH tip:irq/core v1] genirq: remove auto-set of the mask when setting the hint Jesse Brandeburg
2021-05-04 12:15 ` Robin Murphy
2021-05-04 14:29 ` Nitesh Lal
2021-05-04 16:23 ` Jesse Brandeburg
2021-05-17 16:57 ` Nitesh Lal
2021-05-17 17:26 ` Robin Murphy
2021-05-17 18:08 ` Thomas Gleixner
2021-05-17 18:50 ` Robin Murphy
2021-05-17 19:08 ` Thomas Gleixner
2021-05-17 19:43 ` Thomas Gleixner
2021-05-17 20:18 ` Thomas Gleixner
2021-05-17 18:21 ` Nitesh Lal
2021-05-17 19:47 ` Thomas Gleixner
2021-05-17 21:13 ` Nitesh Lal
2021-05-17 20:48 ` Thomas Gleixner
2021-05-17 22:44 ` Nitesh Lal
2021-05-18 0:03 ` Thomas Gleixner [this message]
2021-05-18 0:23 ` Nitesh Lal
2021-05-20 21:57 ` Nitesh Lal
2021-05-21 0:03 ` Nitesh Lal
2021-05-21 11:56 ` Thomas Gleixner
2021-05-21 12:03 ` [PATCH] genirq: Provide new interfaces for affinity hints Thomas Gleixner
2021-05-21 15:45 ` Lijun Pan
2021-05-21 21:45 ` Thomas Gleixner
2021-05-21 16:13 ` Nitesh Lal
2021-05-21 21:48 ` Thomas Gleixner
2021-06-04 20:35 ` Nitesh Lal
2021-05-27 10:03 ` Shung-Hsi Yu
2021-05-27 10:21 ` Shung-Hsi Yu
2021-05-27 13:06 ` Nitesh Lal
2021-05-28 7:20 ` Shung-Hsi Yu
2021-06-07 17:00 ` Nitesh Lal
2021-06-14 16:12 ` Nitesh Lal
2021-05-21 13:46 ` [PATCH tip:irq/core v1] genirq: remove auto-set of the mask when setting the hint Nitesh Lal
2021-05-21 15:15 ` Thomas Gleixner
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